We have mapped and sequenced the 5' termini of adenovirus-2 early and late mRNAs, and their DNA templates. We will evaluate these as viral promoter sequences. An in vitro system for synthesizing late RNA employing isolated nuclei will be used to map the start site for late transcripts. The activation of early and late promoters during the viral life cycle will be measured. The mechanism of the "early-late transcription switch" will be investigated.